Re: Landing speeds

Date:         13 Jul 97 19:52:41 
From:         D.P.Rhodes@lboro.ac.uk (Darren Rhodes)
Organization: Loughborough University
References:   1
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On 18 Jun 97 02:36:57 , Peter Coe <petercoe@bigfoot.com> wrote:

>I was hanging out near SFO at the weekend, and had the opportunity to
>watch a United 777 and a United 737 doing a parallel landing.  The
>thing I found surprising was how much faster the 737 was going.
>I would have said the 737 was at least 10% faster on the approach.
>
>When I first saw them coming in, the 737 was a way behind, and
>much higher, but by touch down the 737 was quite a way ahead,
>
>So what's the deal?  Logic says the bigger they are, the harder
>they fall, but apparently this isn't true with aircraft.

You don't mention which model of 737 but if it was a -400 or even -300
it would explain things. The 737-300/400 is development aircraft and
as such has grown in weight by several tonnes from the original
version yet the wing area has remained unchanged.

In contrast, the 777 has built to be developed, yet the 777-200A is
the basic version and is over-winged. This means Boeing can stretch it
and still retain the same wing (something Airbus cannot with the
A330/A340 developments).

A good comparison is the given by calculating aircraft wing loadings
(MTOW/Wing Area).

Boeing 737-400: 690 kg/sqm
Boeing 777-200A: 536kg/sqm

It is also likely that the 777 was at a relatively low landing weight
relative to its max landing weight compared to the 737.

At max landing weight the approach speeds are:

Boeing 737-400: 138 knots
Boeing 777-200: 138 knots

These of course are the final approach speeds. The 737-400 does as
well as the 777 with a relatively smaller wing because its flaps
produce more lift (but are also heavier).

It is also possible that ATC asked the 737-400 pilot to speed up the
approach.